1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly relates to an image forming apparatus that can effectively conduct image forming process control by controlling a timing for forming an image adjustment pattern and a timing for separating a secondary transfer member from an intermediate transfer member.
2. Discussion of the Related Art
In related art image forming apparatuses with a tandem type configuration, a plurality of image forming devices are provided thereto.
Each of the plurality of image forming devices includes an image bearing member and other image forming components arranged around the image bearing, together with at least one image transfer member, for conducting a series of image forming operations.
Specifically, an image bearing member of each of the plurality of image forming devices is uniformly charged by a charging unit, which is one of the image forming components, and irradiated by a writing unit so as to form an electrostatic latent image on a surface thereof.
The electrostatic latent image formed on the image bearing member is developed by a developing unit, which is also one of the image forming components, into a visible toner image.
The visible toner image on each of the plurality of image forming devices is primarily transferred onto an intermediate transfer member into a full color toner image in an overlaying manner.
The overlaid toner image is electrically attracted by a secondary transfer member at a secondary transfer portion and transferred onto a recording medium, such as a transfer sheet.
The overlaid toner image on the recording medium is fixed by a fixing unit and discharged to a sheet discharging tray.
The above-described operations may be conducted by a related art image forming apparatus with one image bearing member provided thereto.
In this case, the image bearing member receives and develops the toner images one by one for four times according to the number of colors of toner so as to primarily transfer the toner images onto the intermediate transfer member to form an overlaid full color toner image on the intermediate transfer member.
In addition to the image forming operations, the related art image forming apparatus conducts a series of image adjustment operations for adjusting image density, tone, etc.
For conducting the image adjustment operations, the related art image forming apparatus may further include optical sensors.
A plurality of toner patterns for image adjustment (hereinafter, referred to as “image adjustment pattern”) are formed in a non-image forming area on each surface of the plurality of image bearing members.
After the plurality of image adjustment patterns have been transferred onto the intermediate transfer member, the optical sensors provided for each color of toner detect the plurality of image adjustment patterns so that image forming parameters can be optimally adjusted.
In one technique for related art image forming apparatuses provided with optical sensors, the optical sensors are disposed so as to face the intermediate transfer member and arranged at a downstream side of a primary transfer portion in a travel direction of the intermediate transfer member and at an upstream side of a secondary transfer portion in a travel direction of the intermediate transfer member.
However, when the optical sensors are disposed in a face-up manner with respect to the surface of the intermediate transfer member, toner may be scattered from toner images. This can cause incorrect sensing and incorrect detection results.
Further, some distance for arranging the optical sensors may be required between the primary transfer portion and the secondary transfer portion.
These conditions cannot cause a reduction of space and a reduction of time for first print output.
In a different technique for related art image forming apparatuses, optical sensors are disposed at a downstream side of the secondary transfer portion in a travel direction of the intermediate transfer member.
In this case, the secondary transfer member is applied with a bias having a same polarity as toner when a plurality of image adjustment patterns formed on the intermediate transfer member pass by the secondary transfer portion, so that the plurality of image adjustment patterns cannot be transferred to the secondary transfer roller.
Some amount of toner, however, may transfer onto the secondary transfer roller. In addition, the amount of transferred toner may depend on environmental conditions.
For example, when the surface of the secondary transfer roller is contaminated, the backside of a transfer sheet may also be contaminated and/or the plurality of image adjustment pattern may be deformed or skewed enough to obtain an incorrect detection result.
To eliminate the above-described drawbacks, the secondary transfer member can separate from the intermediate transfer member when the plurality of image adjustment patterns pass by the secondary transfer portion.
However, when the plurality of image adjustment patterns are formed while printing a series of images, the intermediate transfer member can cause nonuniformity or unevenness in rotations thereof, and can result in an adverse affect on image quality.
To avoid deformation in the plurality of image adjustment patterns, a secondary transfer member may include a non-contact type transfer member such as corotron. It is, however, easily assumed that a secondary transfer member employing a corotron method can cause an increase of an amount of ozone production. In addition, a different operation may be required for conveying a transfer sheet. These possibilities can increase ineffectiveness in both image forming and adjustment operations.
As described above, in such related art image forming apparatus including a plurality of image forming devices and an intermediate transfer member, image forming process and toner density are controlled by changing image forming conditions and forming a plurality of image adjustment patterns having different amounts of toner.
In this case, it is difficult to conduct a regular image forming operation and an image adjustment operation at the same time. Therefore, the regular image forming operation such as a production of copies and prints may need to be stopped while the image adjustment operation is being conducted.
The time period of stopping the regular image forming operation for the image adjustment operation may be regarded as a downtime for users. Therefore, the downtime may need to be reduced as much as possible.